Supervisory system for a vehicle accelerator pedal travel transducer

ABSTRACT

In a supervisory system (FIG. 7) for the accelerator pedal transducer (26) in an electronic engine control (EMS) for a vehicle engine, the output signal (U-FFG) of the transducer (26) is interpreted to show whether or not the transducer is at or close to the idling position. The resulting information is compared with the states of idling and pressure switches (18, 28) which shows whether or not the accelerator pedal (30) is actually at or close to its idling position. A contradiction resulting from this comparison indicates a fault and remedial action can be taken by the EMS, for example, to reduce the engine power to a precautionary value. A contradiction between other comparisons shows that one of the switches (18, 28) is faulty. In the event of the accelerator pedal sticking in a depressed position after the driver has lifted his foot and depressed the brake (FIG. 5) a brake signal (BS) can be passed through a gating circuit controlled by the idling switch signal (FFG-LL) to produce a reaction signal(RS). The EMS processes the latter to reduce the engine power to a precautionary safe value.

FIELD OF THE INVENTION

The invention relates to a supervisory system for monitoring theaccelerator pedal travel transducer in an electronic control system fora combustion engine

BACKGROUND OF THE INVENTION

An electronic control system to which the invention may be applied isdescribed in an article entitled "Elektronische Motorsteuerung fuerKraftfahrzeuge" published in "MTZ" Motortechnische Zeitschrift, year 46,Vol. 4, 1985, published by Franckh'sche Verlagshandlung Stuttgart. Inthis article, it is explained that electronic engine control (called"EMS" for short) means a system in which the conventional mechanicallinkage between the accelerator pedal and the element (the throttlevalve in a petrol engine or the regulating rod in a diesel injectionpump) determining the engine output is replaced by an electricalconnection comprising a pedal travel transducer (potentiometer) actuatedby the accelerator pedal and an actuator (servomotor) actuating the saidelement.

The above article describes in particular a system (now sometimes called"E-gas") in which the servomotor adjusts the throttle valve incarburetor or petrol injection engine. U.S. Pat. Nos. 4,515,125 and4,509,480 describe supervisory systems of the initially recited kindwhich are used for electronic diesel control (EDC). The two patentspecifications disclose the use of a separate switch for detectingwhether or not the accelerator pedal is in its idling position. The EDCperforms a "signal-range check" to monitor the occurrence of faults inthe operation of the system. Amongst other parameters, the acceleratorpedal position is monitored and, for the purpose of the signal-rangecheck, a separate idling switch, actuated when the accelerator pedal isin its idling position, may be used rather than the pedal traveltransducer. The purpose of carrying out the signal-range check on theaccelerator pedal position is to ensure that appropriate measures aretaken by the EDC to prevent too large an injected fuel quantity if afault should occur in the pedal travel transducer whereby the lattergives a signal corresponding to a substantially greater injectd fuelquantity than is desired by the driver.

Disadvantages of the supervisory systems described in U.S. Pat. Nos.4,515,125 and 4,509,480 are that they cannot respond to all faultconditions and cannot pinpoint faults when they occur, for example, inthe accelerator travel transducer.

SUMMARY OF THE INVENTION

The invention also relates to a supervisory system for monitoringaccelerator pedal travel transducers in an electronic control system fora combustion engine. The system has an idling switch which detects theidling position of the accelerator pedal, in which the actual outputsignal (U-FFG) from the pedal travel transducer is interpreted and iscompared with an output signal to be expected when the accelerator pedalis at or close to the idling position. A fault indication is producedwhen the information obtained from this comparison contradicts the pedalposition information derived from the idling switch.

Such a system is briefly described in EP-A-0109478. However, such asystem lacks reliability in that it does not necessarily fail safe.Should one of the connections to the idling switch be broken, this maynot show up and the supervisory system can then not respond to asticking travel tranducer.

The invention furthermore relates to a supervisory system for theaccelerator pedal travel transducer in an electronic control system fora combustion engine installed in a vehicle. The system has an idlingswitch, which detects the idling position of the accelerator pedal, anda brake switch responsive to actuation of the vehicle brakes.

Such a system is described in U.S. Pat. No. 4,791,900. In

this system the brake switch, which may be the stoplight switch, is usedas a redundant switch for producing a brake signal (BS) which is used tomonitor the operation of the idling switch associated with theaccelerator pedal. Operation of the brake normally implies that thedriver has released the accelerator pedal so that the latter shouldalready be in its idling position. The output signal (LGS) from theidling switch is processed in the EDC in addition to the output signal(U-FFG) from the pedal travel transducer. The brake signal (BS) may alsobe used to switch off automatic velocity control when the EDC isdesigned for such control.

However, it has hitherto not been possible to take appropriate measuresin an EMS in the event of the accelerator pedal sticking in a depressedposition, for example, due to a foot mat being rucked up, or theaccelerator pedal travel transducer sticking, although the latter eventcan be detected if the idling switch is structurally independent of thetravel transducer.

According to a feature of the invention, the idling switch is a pressureswitch actuated by take up of a lost motion travel of the acceleratorpedal from its idling stop before the pedal travel transducer is itselfdisplaced from its idling position. Enhanced redundance is obtainedthrough the use of a pressure switch separate from the traveltransducer. The computer logic can correctly diagnose the locality of afault and in this respect, supervision of the redundant components isimportant as otherwise a fault in the redundant signals would lead to acomplete absence of safety.

A simple arrangement is achieved in that operation of the acceleratorpedal through the above-mentioned lost motion travel is executed againsta relatively light spring force from a stop position to an idlingposition at which the pedal travel transducer begins to respond. Also,no fault in the pedal travel transducer is diagnosed over toleranceranges of triggering of the pressure switch and the output signal(U-FFG) of the travel transducer, in that no fault signal is obtainedover the cumulative transducer output range (U-FFG-MIN to U-FFG-LLO)corresponding to these tolerance ranges whether the pressure switch isopen or closed.

According to another feature of the invention, the system includes anadditional idling switch which is mechanically coupled to or associatedwith the pedal travel transducer. The actual output signal (U-FFG) fromthe pedal travel transducer is interpreted and compared with an outputsignal to be expected when the pedal travel transducer is at or close tothe idling position and a fault indication is produced when the resultof such comparison contradicts the transducer position information (LGS)derived from the idling switch and/or the pedal position information(PDS) obtained from the pressure switch.

According to another embodiment, signals are obtained, whereby thereliability of the supervision is further improved. Although theincreased complexity resulting from the provision of two switches ratherthan one leads to an increased possibility of a fault arising in thesupervisory system itself, e.g., cable faults, it is possible to detecta fault in a switch or in its circuitry and to exclude the defectiveredundant signal during continued monitoring. The driver can thereby bewarned of the presence of a fault but can carry on driving normally withcontinued supervision of the pedal travel transducer.

An improved system for detecting the sticking of the accelerator pedalin a depressed position is obtained in that the outputs (FFG-LL, BS) ofthe idling and/or pressure switch and a brake switch responsive toactuation of the vehicle brakes are compared to produce a reactionsignal (RS1) if the accelerator pedal, or at least the accelerator pedaltravel transducer is remote from its idling position when the brakes areactuated. An improved system for detecting the sticking of theaccelerator pedal in a depressed position is also obtained in that theoutputs (BS, FFG-LL) of the two switches are compared to produce areaction signal (RS) if the accelerator pedal or at least theaccelerator pedal travel transducer is remote from its idling positionwhen the brakes are actuated.

Preferably, the reaction signal is used to reduce the engine power towhat is considered to be a safe value, in that the electronic enginecontrol so responds to the reaction signal (RS1) that the engine poweris thereby reduced to a predetermined safe value Q_(s).

It is recommended that the reaction signal be effective to reduce thepower output only after a short delay in that the electronic enginecontrol so responds to the reaction signal (RS1) that the engine poweris thereby reduced, if the engine speed is above a safe value and theengine speed is controlled down to this safe value. Also, it isadvantageous to reduce power along a ramp in that the electronic enginecontrol only responds to the reaction signal (RS1) after a delay time.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described, by way of example, with reference tothe accompanying drawings, in which:

FIG. 1 is a circuit diagram of a supervisory system for monitoring anaccelerator pedal travel transducer,

FIG. 2 is a graph relating to the embodiment of FIG. 1 in which thetransducer output is plotted against the detected travel,

FIG. 3 is a diagrammatic illustration of the arrangement of a pressureswitch in accordance with the invention,

FIG. 4 is a graph, similar to FIG. 2, but relating to the embodiment ofFIG. 3,

FIG. 5 is a circuit diagram of a supervisory system for monitoringsticking of the accelerator pedal,

FIG. 6 is a graph illustrating the operation of the system of FIG. 5,

FIG. 7 is a circuit diagram of an embodiment of a supervisory systememploying two redundant signals,

FIG. 8 is a diagram of a circuit for checking whether a pedal pressureswitch has stuck in the idling position,

FIG. 9 is a diagram of a circuit for checking whether the pedal pressureswitch has stuck in the full or partial load position, and

FIG. 10 is a graph, similar to that of FIG. 2, but relating to theembodiment of FIGS. 7 to 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a supervisory system for the accelerator pedal 10 of anelectronic engine control (EMS) for a mechanically propelled vehicle.The EMS includes a main computer 12 by means of which the engine poweris controlled in accordance with the position of the accelerator pedal10 and in accordance with operating parameters, such as engine speed.Such an EMS for a diesel engine is described in U.S. Pat. No. 4,791,900and one for a petrol engine is briefly described in the above-mentionedarticle by Gerhard Kolberg.

The accelerator pedal 10 is mechanically coupled to the slider 14 of apotentiometer 16 which serves as the accelerator pedal traveltransducer. The ends of the potentiometer are connected between a 5 Vsource and earth in the main computer 12 and the pedal position signalU-FFG appearing on the slider 14 is processed in the computer 12 to setthe injected fuel quantity in the case of a diesel engine or to set theair inlet throttle valve in the case of a petrol engine, in accordancewith the driver's wishes.

The accelerator pedal 10 is also mechanically coupled to an "idling"switch 18 one pole of which is connected via a resistor 20 in thecomputer 12 to a 5 V source and the other pole of which is connected toearth. The switch 18 is a normally-closed switch and is opened as soonas the accelerator pedal 18 has been depressed a short distance. Thus anidling position signal FFG-LL appears as earth potential on the terminalLGS of the resistor 20 when the pedal 10 is at or very close to itsidling position whereas a pedal-actuated signal FFG-LL appears as a 5 Vpotential on the resistor terminal LGS when the driver depresses theaccelerator. The idling switch 18 is used to monitor the operation ofthe pedal travel transducer 16.

As shown in FIG. 2, the transducer output voltage U-FFG is proportionalto the position of the slider 14 which is dependent on the depression ofthe accelerator pedal. This output voltage is divided into five ranges,namely

range 1: U-FFG<U-FFG-MIN

range 2: U-FFG-MIN<U-FFG<U-FFG-LLU

range 3: U-FFG-LLU<U-FFG<U-FFG-LLO

range 4: U-FFG-LLO<U-FFG<U-FFG-MAX

range 5: U-FFG-MAX<U-FFG

where U-FFG-MIN and U-FFG-MAX are the transducer output voltages whenthe accelerator pedal is against its idling and full load stops,respectively, and U-FFG-LLU and U-FFG-LLO are the transducer outputvoltages at the minimum and maximum ends of the tolerance range for theopening or closing of the idling switch in relation to the transduceroutput voltage U-FFG during the first part of the pedal travel away fromits idling stop. Table 1 is a plausibility diagram representing theoperation of the supervisory system of FIG. 1.

                  TABLE 1                                                         ______________________________________                                        actual                                                                        transducer                                                                    output                                                                        voltage   idling    processed value                                           (U-FFG)   switch    or symptom  diagnosis                                     ______________________________________                                                      LL          idling speed                                                                            faulty transducer                          range 1                                                                                                (optional)                                                         ##STR1##    elevated idling                                                                         faulty transducer                                                  speed                                                             LL          U-FFG     --                                         range 2                                                                                     ##STR2##    elevated idling                                                                         faulty transducer                                                  speed     or faulty switch                                        LL                                                               range 3                                                                                                 U-FFG     --                                                      ##STR3##                                                                     LL          elevated idling                                                                         faulty transducer                          range 4                                                                                                speed     or faulty switch                                         ##STR4##    U-FFG     --                                                     LL          idling speed                                                                            faulty transducer                          range 5                                                                                                (optional)                                                         ##STR5##    elevated idling                                                                         faulty transducer                                                  speed                                               ______________________________________                                    

Table 1 demonstrates the ability of the supervisory system to respond tofaults in the pedal transducer and in the idling switch, provided thatthe idling switch switches over within the prescribed tolerance band andprovided that the output voltage U-FFG of the pedal transducer is withinthe prescribed tolerance band for all positions of its slider. This lastfeature is not shown in FIG. 2 but may be deduced therefrom. In knownsystems it is not possible to detect the fault that the idling switchhas stuck in its full load position.

It is advantageous from the point of view of likelihood of failure thatthe idling switch 18 closes to earth in the idling position and isconnected via a resistor 20 to a voltage source (failure mode andeffects analysis).

In relation to a pure signal-range check, improved emergency or stand-bydriving conditions can be obtained, in that a speed at least betweenidling and elevated idling can be selected when there is a signal-rangefault with the redundant signal (optional digital function indicated inTable 1).

In FIGS. 1 and 2 and in Table 1, it is assumed that the idling switch isdirectly coupled to the accelerator pedal travel transducer, whereby thelatter must be displaced slightly from its idling position before theidling switch is actuated. A higher degree of redundance can be obtainedby making the idling position switch 28 completely separate from thetravel transducer 26, as shown in FIG. 3. The accelerator pedal 30 ismade separate from a pedal lever 32 and acts on the latter via theidling position switch 28, which is hereinafter referred to as apressure switch, inasmuch as it is responsive to pressure applied to thepedal 30. The pedal lever 32 acts via a connecting rod 34 on the slider24 of the potentiometer 26, serving as the travel transducer. A lightreturn spring 36 acts between the pedal lever 32 and the pedal 30.

Initially, the pedal 30 is in a position, as shown, which can be said tobe a position below idling position. When the driver first depresses thepedal 30, an initial tolerance clearance between the pedal 30 and thepressure switch 28 which is shown mounted on the lever 32 is taken up.Further depression of the pedal 30 actuates the pressure switch 28. Onlyafter the switch travel is taken up does the pedal lever 32 begin tomove and thereby displace the travel transducer 26 from its idlingposition. The effect is shown in the graph of FIG. 4 and Table 2 below,wherein the symbols have the same meaning as in FIG. 2 and Table 1.

                  TABLE 2                                                         ______________________________________                                        actual                                                                        trans-                                                                        ducer                                                                         output                                                                        voltage pres-                                                                 (U-     sure      processed value                                             FFG)    switch    or symptom    diagnosis                                     ______________________________________                                                    LL          idling speed*                                          range 1                                                                                                             faulty transducer                                   ##STR6##    elevated idling                                                              speed                                                             LL                                                                 range 3                 U-FFG         --                                                  ##STR7##                                                                     LL          elevated idling                                                                             faulty transducer*                       range 4                speed*                                                             ##STR8##    U-FFG         --                                                 LL          idling speed*                                          range 5                                                                                                             faulty transducer                                   ##STR9##    elevated idling                                                              speed                                                 ______________________________________                                         These symptoms or diagnosis only apply in the case wherein the idling         position switch is perceived as being intact                             

Because the pressure switch 28 and the potentiometer 26 are mechanicallyindependent of one another, a sticking potentiometer slider 24 can bedetected in that the return spring 36 releases the switch 28 when thedriver lifts his foot from the pedal 30.

A disadvantage as compared with the embodiment of FIGS. 1 and 2 is thatit is not possible to arrange for the actuation or triggering of thepressure switch to take place at a transducer output voltage U-FFGslightly above the idling value U-FFG-LL because only a limit switch canbe used to achieve the objects of the embodiment of FIGS. 3 and 4.

For a complete supervision of the redundance, a special logic circuit isneeded in order to identify the location of a fault unambiguously.

The circuit of FIG. 5 can be used to supervise the dynamic operation ofthe accelerator pedal travel transducer 16,26. This is achieved bymonitoring a brake actuation signal BS to ascertain whether the brakesare applied (implying that the driver requires the idling power output)when the accelerator pedal is not in its idling position, for example,due to it being held depressed or partly depressed by a rucked mat.

To this end, a braking signal BS, which may be produced by the usualbrake light switch, and the idling position signal FFG-LL, meaning theaccelerator pedal is not in its idling position, are fed to an AND gate40. The output of the AND gate 40 is fed via another AND gate 42 and adelay circuit 44 to provide a reaction signal RS1. The output of the ANDgate 40 is also applied to the input T of an integrator in the form of acounter 46 whose output Q is connected to a second input of the AND gate42. The signal U-FFG from the accelerator pedal travel transducer is fedto the input of a differentiator 48 whose output is applied via arectifier gate 50 to the reset input R of the counter 46.

FIG. 6 is a graph in which injected fuel quantity Q is plotted againsttime and shows the operation of the circuit of FIG. 5 in the case of adiesel engine. It is assumed that the EMS is operative to deliver theinjected fuel quantity Q_(i) desired by the driver, which quanity islarger than the precautionary quantity Q_(s) described below. At instantT₁, it is assumed that the driver lifts his foot from the acceleratorpedal and applies the brake but that the accelerator pedal sticks in adepressed condition. The instant T₁ is thus the onset of a faultcondition. The brake signal BS is passed by the AND gate 40 because the"inverted" idling position signal FFG-LL is still applied to the otherinput of this AND gate reaches the delay circuit 44. After apre-programmable delay of, say, 2 seconds a reaction signal RS1 isproduced at instant T₂ and is processed by the EMS, whereby the injectedfuel quantity Q is reduced to a pre-programmed precautionary value Q_(s)which is considered to be safe and to enable the vehicle to keep moving.According to an alternative function, the fuel quantity is reduced ifthe engine speed is above a value which is considered to be safe and theidling speed is controlled to this value.

The effect of the counter 46 is to cause the injected fuel quantity todecreased in a ramp-like manner so that the precautionary injectedquantity Q_(s) is not reached until instant T₃. The purpose of this rampis to prevent the driver being startled by a sudden reduction ininjected fuel quantity.

If the driver again depresses the accelerator pedal beyond its stuckposition at the instant T₄ with the intention to increase the injectedfuel quantity, the differentiator 48 supplies a signal to the resetinput R of the counter 46. The latter causes the injected fuel quantityto rise again in a pre-programmable ramp-like manner, whereby theinjected quantity returns to the value Q_(i) intended by the driver onlyat the instant T₅.

The rectifier gate 50 prevents the safety conditions being removed inthe event that the accelerator pedal releases itself, e.g., upon removalof the rucked footmat, whereby the injected fuel quantity cannot beincreased above its precautionary value Q_(s) until the driver againdepresses the accelerator pedal.

It is irksome for the driver to have to drive no faster than therelatively low speed achievable with the above-mentioned precautionaryinjected fuel quantity Q_(s) which corresponds to a quantity onlyslightly above the idling quantity. This disadvantage can be avoided byusing two redundant signals, as shown in FIG. 7, whereby two faults mustoccur in the supervisory circuits before the driving conditions areadversely effected. The circuit shown in FIG. 7 employs the pressureswitch (28) of FIG. 3, which is mechanically actuated by thepotentiometer slider 24 of FIG. 1 and also the idling switch 18 of FIG.1.

As described with reference to FIG. 6, the effect of a fault in theidling switch 18 or in the pressure switch 28 is to cause the injectedfuel quantity to be reduced to a relatively low safe value Q_(s) in aramp-like manner. The circuits shown in FIGS. 8 and 9 are designed toenable the engine to return to normal operation in the event ofdetection of a fault in the pressure switch 28.

The circuit of FIG. 8 is designed to produce a reaction signal RS2 ifthe pressure switch 28 of FIG. 7 should fail to return to its no-loadposition. Should the signal BS from the brake light switch, the signalLGS-LL from the idling switch 18 and a signal from a comparator 60 whichcompares the transducer output U-FFG with a voltage U-FFG MINcorresponding to a speed slightly above idling, all indicate that thedriver is braking, that the output of the pedal travel transducer 26corresponds to the idling position and that the pedal travel transduceris actually in its idling position, and should the signal PDS-LL fromthe pressure switch 28 suggest that the pedal is depressed, an AND gate62 delivers an output to an integrator 64. After an adjustable totaldelay of 5 sec to 2 min obtained by means of the integrator 64, thereaction signal RS2 is produced and causes the main computer 12 todisregard the signal from the pressure switch 28. At the same time, thedriver is warned of the faulty switch. Should the fault be removed, forexample by re-positioning a rucked footmat, the idling position signalPDS-LL from the pressure switch 28 re-sets the integrator 64.

The circuit of FIG. 9 is designed to produce a reaction signal R3 shouldthe pressure switch 28 indicate a no-load position even when theaccelerator pedal 30 is depressed towards its full load position. Acomparator 66 compares the transducer output U-FFG with a referencevoltage UR to produce a signal when the pedal travel transducer 26indicates a pedal position of at least, say, 50% of full load. Shouldthe signal PDS-LL from the pressure switch 28 suggest that the pedal 30is in its no-load position, and AND gate 68 delivers a signal to acounter 70. Should there be several, say two, occasions when thiscontradiction occurs, the counter 70 delivers a reaction signal RS3which is used by the computer 12 to cause the injected fuel quantity torise from the precautionary value Q_(S), to which it will havepreviously been set as described with reference to FIGS. 5 and 6, to itsintended value Q_(i) in a ramp-like manner. At the same time, the driveris warned of the defective pressure switch. Should the defect beremoved, a signal PDS-LL indicative that the pressure switch is not inits no-load position resets the counter 70.

Instead of or in addition to the output of the comparator 66, the signalLGS-LL, indicating that the pedal travel transducer 26 is not in itsno-load or idling position, can be fed to the AND gate 66, as indicatedby a dotted line.

The function of the circuits of FIGS. 8 and 9 is to indicate that thepressure switch 28 of FIG. 7 is intact by means of agreement between thepedal travel transducer voltage, the idling switch and the pressureswitch over one plausibility phase above no-load and in no-load. FIG. 10is graph and Table 3 is a plausibility diagram, representing operationof the supervisory system of FIG. 7. Table 4 is a plausibility diagramshowing optional modifications which can be made for range 1 to range 5.

                                      TABLE 3                                     __________________________________________________________________________    actual transducer                                                             output voltage                                                                           idling                                                                            pressure                                                                           processed value                                           (U-FFG)    switch                                                                            switch                                                                             or symptom    diagnosis                                   __________________________________________________________________________    range 1    X   X    elevated idling speed                                                                       faulty transducer                                      LL  LL   U-FFG         --                                                      LL                                                                                ##STR10##                                                                          U-FFG         --                                         range 2                                                                                   ##STR11##                                                                         LL   elevated idling speed                                                                       faulty idling switch                                   ##STR12##                                                                         ##STR13##                                                                          elevated idling speed                                                                       faulty transducer                                     LL  LL   elevated idling speed                                                                       faulty pressure switch                                  LL                                                                                ##STR14##                                                                          U-FFG         --                                         range 3                                                                                   ##STR15##                                                                         LL   elevated idling speed                                                                       faulty pressure switch                                 ##STR16##                                                                         ##STR17##                                                                          U-FFG         --                                                    LL  LL   elevated idling speed                                                                       faulty transducer                                       LL                                                                                ##STR18##                                                                          U-FFG; limited fuel quantity                                                                faulty idling switch                       range 4                                                                                   ##STR19##                                                                         LL   elevated idling speed                                                                       faulty pressure switch                                 ##STR20##                                                                         ##STR21##                                                                          U-FFG         --                                         range 5    X   X    elevated idling speed                                                                       faulty transducer                           __________________________________________________________________________

                                      TABLE 4                                     __________________________________________________________________________    actual transducer                                                             output voltage                                                                           idling                                                                            pressure                                                                           processed value                                           (U-FFG)    switch                                                                            switch                                                                             or symptom    diagnosis                                   __________________________________________________________________________               LL  LL   normal idling speed                                                                         --                                           range 1                                                                                  ##STR22##                                                                         ##STR23##                                                                          elevated idling speed                                                                       faulty transducer                                     LL  LL   U-FFG         --                                                      LL                                                                                ##STR24##                                                                          U-FFG         --                                         range 2                                                                                   ##STR25##                                                                         LL   elevated idling speed                                                                       faulty idling switch                                   ##STR26##                                                                         ##STR27##                                                                          elevated idling speed                                                                       faulty transducer                                     LL  LL   elevated idling speed                                                                       faulty pressure switch                                  LL                                                                                ##STR28##                                                                          U-FFG         --                                         range 3                                                                                   ##STR29##                                                                         LL   elevated idling speed                                                                       faulty pressure switch                                 ##STR30##                                                                         ##STR31##                                                                          U-FFG         --                                                    LL  LL   elevated idling speed                                                                       faulty transducer                                       LL                                                                                ##STR32##                                                                          U-FFG; limited fuel quantity                                                                faulty idling switch                       range 4                                                                                   ##STR33##                                                                         LL   elevated idling speed                                                                       faulty pressure switch                                 ##STR34##                                                                         ##STR35##                                                                          U-FFG         --                                                    LL  LL   normal idling speed                                                                         faulty transducer                            range 5                                                                                  ##STR36##                                                                         ##STR37##                                                                          elevated idling speed                                                                       faulty transducer                          __________________________________________________________________________

In the event of a defect in the pressure switch being diagnosed, thesignal from the pressure switch is ignored. In the event of a furtherdefect, the injected fuel quanity is limited to the precautionary value.

We claim:
 1. A supervisory system for monitoring an accelerator pedaltravel transducer in an electronic control system for a combustionengine, the system comprising:an idling pressure switch for detectingthe idling position of the accelerator pedal; means for actuating saidpressure switch by taking up lost motion travel of the accelerator pedalfrom said idling position before said pedal transducer is displaced fromsaid idling position; means for providing an additional idle positionsignal; composite means having respective inputs for receiving saidadditional idle position signal, the signal of said idling pressureswitch and the signal of said accelerator pedal transducer; and, saidcomposite means being provided for generating an alarm signal inresponse to said signals applied to said inputs when at least one ofsaid signals applied to said inputs is not plausible to the remainingones of said signals applied to said inputs.
 2. The supervisory systemof claim 1, wherein the operation of the accelerator pedal through saidlost motion travel is executed against a relatively light spring forcefrom a stop position to an idling position at which the pedal transducerbegins to respond.
 3. The supervisory system of claim 1, wherein areaction signal (RS3) is produced when the signal (PDS-LL) from thepressure switch indicates that the accelerator pedal is released,whereas at least one other signal (U-FFG, LGS-LL) indicates that theaccelerator pedal is in at least one of a part load position and a fullload position, and this reaction signal (RS3) is used to cause thesignal (LGS-LL) from the pressure switch to be disregarded whendetermining whether there is a fault on the pedal travel transducer. 4.The supervisory system of claim 1, wherein the idling switch is closedin the idling position of at least one of the accelerator pedal and thepedal travel transducer and the pressure switch is open in said idlingposition.
 5. A supervisory system for monitoring an accelerator pedaltravel transducer in an electronic control system for a combustionengine, the system comprising:an idling pressure switch for detectingthe idling position of the accelerator pedal; means for actuating saidpressure switch by taking up lost motion travel of the accelerator pedalfrom said idling position before said pedal transducer is displaced fromsaid idling position; and, no fault in the pedal travel transducer beingdiagnosed over tolerance ranges of triggering of the pressure switch andthe putput signal (U-FFG) of the travel transducer, in that no faultsignal is obtained over the cumulative transducer output range(U-FFG-MIN to U-FFG-LLO) corresponding to these tolerance ranges whetherthe pressure switch is open or closed.
 6. A supervisory system formonitoring an accelerator pedal travel transducer in an electroniccontrol system for a combustion engine, the system comprising:an idlingpressure switch for detecting the idling position of the acceleratorpedal; means for actuating said pressuree switch by taking up lostmotion travel of the accelerator pedal from said idling position beforesaid pedal transducer is displaced from said idling position; and, anadditional idling switch which is operatively connected to the pedaltravel transducer, the actual output signal (U-FFG) from the pedaltravel transducer being interpreted and compared with an output signalto be expected when the pedal travel transducer is at least close to theidling position and a fault indication is produced when the result ofsuch comparison contradicts at least one of the transducer positioninformation (LGS) derived from the idling switch and the pedal positioninformation (PDS) obtained from the pressure switch.
 7. The supervisorysystem of claim 6, wherein a reaction signal (RS2) is produced when thesignal (PDS-LL) from the pressure switch indicates that the acceleratorpedal is not in its idling position, whereas at least two other signals(BS, LGS-LL, U-FFG) indicate that the accelerator pedal is at leastclose to its idling position, and this reaction signal (RS2) is used tocause the signal (LGS-LL) from the pressure switch to be disregardedwhen determining whether there is a fault on the pedal traveltransducer.
 8. The supervisory system of claim 7, wherein a brakepressure signal (BS), indicative that the brakes are applied, is used toindicate that the accelerator pedal is in its idling position.
 9. Thesupervisory system of claim 7, further comprising an integrator fordelaying production of the reaction signal (RS2) by an adjustableperiod.
 10. The supervisory system of claim 7, wherein a brake pressuresignal (BS), indicative that the brakes are applied, is used to indicatethat the accelerator pedal ought to be in its idling position.
 11. Asupervisory system for monitoring an accelerator pedal travel transduceris an electronic control system for a combustion engine, the systemcomprising:an idling pressure switch for detecting the idling positionof the accelerator pedal; means for actuating said pressure switch bytaking up lost motion travel of the accelerator pedal from said idlingposition before said pedal transducer is displaced from said idlingposition; a reaction signal (RS3) is produced when the signal (PDS-LL)from the pressure switch indicates that the accelerator pedal isreleased, whereas at least one other signal (U-FFG, LGS-LL) indicatesthat the accelerator pedal is in at least one of a part load positionand a full load position, and this reaction signal (RS3) is used tocause the signal (LGS-LL) from the pressure switch to be disregardedwhen determining whether there is a fault on the pedal traveltransducer; and, a counter for counting instances of contradictionbetween the pressure switch signal (PDS-LL) and at least one of thesignals (U-FFG, LGS-LL) to postpone production of the reaction signal(RS3) until there have been at least two, such instances.
 12. Asupervisory system for monitoring an accelerator pedal travel transducerin an electronic control system for a combustion engine, the systemcomprising:an idling switch for detecting the idling position of theaccelerator pedal; means for interpreting the actual output signal(U-FFG) from the pedal travel transducer and comparing said actualoutput signal (U-FFG) to an output signal to be expected when theaccelerator pedal is at least close to the idling position and forproducing a fault indication when the information obtained from thecomparison contradicts the pedal position information derived from theidling switch; and, said idling switch being closed in the idlingposition of at least one of the accelerator pedal and the pedal traveltransducer.
 13. The supervisory system of claim 12, wherein the idlingswitch is arranged to be triggered from one state to the other at aposition at which the output signal U-FFG of the pedal travel transduceris relatively close to the value U-FFG-MIN obtained when the pedal isagainst its idling stop.
 14. The supervisory system of claim 13, whereinno fault in the pedal travel transducer is diagnosed over a tolerancerange of triggering of the idling switch in that no fault signal isobtained over the transducer output range corresponding to thistolerance range, whether the idling switch is open or closed.
 15. Thesupervisory system of claim 14, wherein a fault signal is obtained whenthe pedal travel transducer output (U-FFG) is at a value below the lowertolerance range value (U-FFG-LLU) and simultaneously the idling switchoutput signal (LGS) indicates that the accelerator pedal is not in itsidling position.
 16. The supervisory system of claim 12, wherein theidling switch is integrated into the pedal travel transducer.
 17. Thesupervisory system of claim 12, wherein a fault signal is obtained whenthe output (U-FFG) of the pedal travel transducer is below a lower value(U-FFG-MIN) irrespective of the position of at least one of the idlingswitch and the pressure switch.
 18. The supervisory system of claim 12,wherein a fault signal is obtained when the output (U-FFG) of the pedaltravel transducer is above an upper value (U-FFG-MAX), irrespective ofthe position of at least one of the idling switch and the pressureswitch.
 19. The supervisory system of claim 12, wherein the outputs(FFG-LL, BS) of at least one of the idling switch and the pressureswitch and the output of a brake switch responsive to actuation of thevehicle brakes are compared to produce a reaction signal (RS1) if atleast one of the accelerator pedal and the accelerator pedal traveltransducer is remote from its idling position when the brakes areactuated.
 20. A supervisory system for monitoring an accelerator pedaltravel transducer in an electronic control system for a combustionengine installed in a vehicle, the system comprising:an idling switchfor detecting the idling position of the accelerator pedal and forproducing an idling switch output signal; a brake switch for respondingto the actuation of the brakes of the vehicle and for producing a brakeswitch output signal; and, means for comparing said idling switch outputsignal and said brake switch output signal to produce a reaction signalif at least one of the accelerator pedal and the accelerator pedaltravel transducer is remote from its idling position when the brakes areactuated.
 21. The supervisory system of claim 20, wherein the electronicengine control so responds to the reaction signal (RS1) that the enginepower is thereby reduced to a predetermined safe value Q_(S).
 22. Thesupervisory system of claim 20, wherein the electronic engine control soresponds to the reaction signal (RS1) that the engine power is therebyreduced if the engine speed is above a safe value and the engine speedis controlled down to this safe value.
 23. The supervisory system ofclaim 21, wherein the electronic engine control only responds to thereaction signal (RS1) after a delay time.
 24. The supervisory system ofclaim 21, wherein the engine power is gradually reduced by theelectronic engine control in response to the reaction signal (RS1). 25.The supervisory system of claim 21, wherein the reaction signal (RS1) isdiscontinued in response to a change in the output (U-FFG) of theaccelerator pedal travel transducer.
 26. The supervisory system of claim25, wherein the reaction signal (RS1) is discontinued only in responseto an increase in the transducer output (U-FFG) but not in response to adecrease.
 27. The supervisory system of claim 25, wherein the enginepower is gradually increased by the electronic engine control followingdiscontinuance of the reaction signal (RS1).